Our studies on the mechanism of renin release and on the role of the endocrine kidney in hypertension will be continued and extended. For the elucidation of the mechanism of renin secretion, various model in vivo and in vitro systems including those developed in our laboratory will be utilized. They include animal models, tissue slice preparations from kidneys and submaxillary glands, cell suspension systems, renin secretory grannules, and a radioimmunoassay procedure recently developed in our laboratory for the direct measurement of renin in biological fluids. The in vitro procedures will be used to investigate the mechanism of renin secretion at the cellular and subcellular level in the absence of neurogenic and hemodynamic influences and to study the mechanism of action of various agents known to affect renin release in the intact organism. The results will be important in our understanding of the mechanism of renin release, the etiology of hypertension, and they could help develop better approaches for the diagnosis and treatment of hypertension and cardiovascular diseases. BIBLIOGRAPHIC REFERENCES: Michelakis, A.M. The preparation of renal-cell suspensions for the study of renin production and other renal functions. Methods in Enzymology 39: 20, 1975. Hollifield, J., D. Page, C. Smith, A.M. Michelakis, E. Staab, and R. Rhamy. Renin secreting clear cell carcinoma of the kidney. Arch. Int. Med. 135: 859, 1975.